server.properties explained: the settings worth changing

What the main settings in server.properties do, their defaults, and which ones Cobbly manages for you.

server.properties is the main settings file of every Minecraft server: game mode, difficulty, PvP, the message players see in their server list, and dozens more. On Cobbly you edit it from the Properties tab — a searchable form grouped by topic, with a Raw File view if you prefer the plain text. Changes are saved straight away and take effect the next time the server starts.

This page covers the settings people actually change, what each does, and its default. Values are written exactly as they appear in the file.

Gameplay

gamemode — the mode new players join in: survival (default), creative, adventure or spectator. It only applies to players joining for the first time, unless force-gamemode is on.
force-gamemode — true puts every player back into the default game mode each time they join. Default false.
difficulty — peaceful, easy (default), normal or hard. Can also be changed in game with /difficulty.
hardcore — true makes a death permanent: players are put into spectator mode instead of respawning. Default false. Best decided before a world is created.
pvp — whether players can damage each other. Default true.
allow-flight — whether players flying in survival are allowed. Default false, which kicks them for flying. Turn it on for modpacks with jetpacks, rings of flight or similar — otherwise Minecraft kicks players for using them.
enable-command-block — whether command blocks work. Default false.
spawn-protection — the radius around world spawn where only operators can build. Default 16; set it to 0 to turn it off, which is what most small servers want.
player-idle-timeout — minutes before an idle player is kicked. Default 0, meaning never.

Your server in the list

motd — the "message of the day" shown under your server’s name in the Minecraft server list. Supports colour codes with the § symbol, like §a for green.
resource-pack — a direct download link to a resource pack players are offered when they join.
require-resource-pack — true disconnects players who decline the pack. Default false.
resource-pack-prompt — a custom message shown with the resource pack offer.

World generation

These only matter when a world is created. Changing them later does nothing to terrain that already exists — to use them, reset the world from the World tab, which has its own fields for seed, world type and structures. See How to reset your Minecraft world.

level-seed — the seed. Leave it blank for a random world.
level-type — minecraft:normal (default), minecraft:flat, minecraft:large_biomes or minecraft:amplified.
generate-structures — villages, temples, strongholds and so on. Default true.
level-name — the name of the world folder. Leave it as world: world upload, download and reset all expect that name.

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Access and security

white-list — turns the whitelist on. It is easier to manage from the Players tab, where the same switch is called Relay wake gate — it also decides who can wake a sleeping server. See Controlling who can join.
enforce-whitelist — true kicks players who are online but not on the whitelist the moment it is reloaded, not just at their next join.
online-mode — true (default) checks every player with Mojang’s account servers. Setting it to false lets anyone join under any name. Read Minecraft server offline mode before touching it.

Settings Cobbly manages for you

A few settings are reset by Cobbly every time the server starts. You can edit them, but your change will not stick — they either depend on the machine your server lands on, or they are the limits that keep shared hardware fair:

server-port, enable-rcon, rcon.port, rcon.password, enable-query and query.port — set per start, because a free server can run on a different machine each time it wakes. Your address stays the same regardless.
view-distance and simulation-distance — capped at 6. They are the biggest memory and CPU levers in the game, and on shared hardware one server set to 32 would slow down everyone else’s.
max-players — up to 10 on the free tier.

The full list of numbers is in What are the limits on a free server?.

Editing tips

Restart after saving — the file is only read when the server starts.
In the Raw File view, each line is key=value with no spaces around the =, and true/false in lower case.
Values the game does not recognise are usually ignored silently, so if a change seems to do nothing, check the spelling first.